Hypericin is a constituent of plants belonging to the genus Hypericum. It was isolated from this natural source in a chemically pure state by H. Brockmann et al. (Ann. 1942, 553, 1). Hypericin appears in nature accompanied by the chemically related compound pseudo-hypericin.
The isolation of hypericin from Hypericum plants is not practical on a larger scale, because it requires a lengthy procedure involving extraction with large volumes of solvents and cumbersome chromatographic separations on silica gel columns. The main difficulty in obtaining hypericin in a pure state from the plant material resides in its separation from the accompanying pseudohypericin. This necessitates the aforementioned chromatography with the elution of a large number of fractions, only a few of which contain the pure desired material. The yield of hypericin from the plants is very low, not more than 0.3%, based on the dry plant material.
U.S. Pat. No. 5,120,412 ('412 patent) to Mazur et al., which is incorporated herein by reference, discloses a process for synthesizing hypericin from emodin. The process involves first converting emodin to emodin anthrone which is then dimerized to form protohypericin. The protohypericin is then converted to hypericin by visible light irradiation. This process, however, produces low yield and purity of the final product.
Therefore, there remains a need for a process capable synthesizing hypericin in high yield and high purity.